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1 SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH HOOKWORM INFECTIONS OF SCHOOLCHILDREN IN SOUTHERN THAILAND Malinee T Anantaphruti, Wanna Maipanich, Chatree Muennoo, Somchit Pubampen and Surapol Sanguankiat Department of Helminthology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand Abstract. A study of hookworm infections of schoolchildren was conducted in Nakhon Si Thammarat Province, southern Thailand. Of the, hookworms that were recovered from the children, almost all (.%), were Necator americanus, only three (.%) were identified as Ancylostoma duodenale, and all were female worms. An estimation of the worm burden of and the worm expulsion from the schoolchildren indicated there were cases of light intensity hookworm infection. Fifteen cases (88.%) expelled worms in numbers that corresponded with the worm burden that was estimated from the number of eggs per gram of feces. Two cases (.8%) expelled more worms than predicted. In moderate intensity cases, five (.%) expelled worms in a quantity that corresponding with the estimated worm burden. Eleven cases (8.%) expelled fewer worms than predicted. All cases of heavy intensity infection expelled fewer worms than predicted. INTRODUCTION Soiltransmitted helminthiases are a worldwide public health problem and are especially troublesome in tropical and subtropical regions. Thailand, a subtropical country, faces the same problem: it was found that.% of the total population of Thailand were infected with one or more helminths, the most common of which was hookworm, with a prevalence of.% (Jongsuksantikul et al, ). Ancylostoma duodenale, an oldworld hookworm and Necator americanus, a newworld hookworm, are the major human hookworms. A. ceylanicum, a zoonotic hookworm of dogs and cats, is a cause of minor hookworm infection in humans. According to Beaver et al (8), N. americanus is distributed in tropical and subtropical climates: the southern United States, Caribbean islands, Central America, and northern South America; the worm predominates in central and Correspondence: Dr Malinee Thairungroj, Department of Helminthology, Faculty of Tropical Medicine, Mahidol University, / Rajvithi Road, Bangkok, Thailand. Fax: southern Africa, southern Asia, Melanesia and Polynesia. A. duodenale is found in subtropical and warm temperate climates: southern Europe, the north coast of Africa, northern India, northern China, Japan, Malaysia, and Taiwan. A. ceylanicum is found in tropical and semitropical regions. The southern part of Thailand is known to be endemic for soiltransmitted helminthiases. Hookworm infection has been a public health problem for several decades. Its prevalence has been reported as.% (Vajrasthira and Harinasuta, );.% (Preuksaraj et al, 8); 8.% (Yokogawa et al, 8);.% (Jongsuksantikul et al, );.8% (Muennoo et al, 8). Radomyos and Saovakontha (8), and Harinasuta and Areekul (8), identified adult hookworms in patients admitted to the Hospital for Tropical Diseases, Bangkok: N. americanus 8.% and 8.%; A. duodenale.8% and.%; and A. ceylanicum.% and.%; respectively. The prevalence of A. ceylanicum in the patients was.% (Harinasuta and Areekul, 8). In Nakhon Ratchasima Province, northeast Thailand, Harinasuta and Areekul (8) re 8 Vol No. September

2 HOOKWORM INFECTIONS IN SOUTHERN THAILAND ported that after drug administration,.% of hookworms recovered were Necator americanus and.% were A. duodenale; there were no examples of A. ceylanicum. A. ceylanicum is a common hookworm of dogs and cats throughout the world. It was first recorded in Thailand by Kerr () among the prisoners of Chiang Mai jail. Harinasuta and Areekul (8) reported that % of dogs in Bangkok were infected with A. ceylanicum. In Prachinburi Province, % of cats harbored A. ceylanicum, with the maximum number of worms per cat being 8 (Setasuban et al, ). A. ceylanicum was found in dogs in Bangkok during the period 8: the infection rate was.% (Anantaphruti et al, ). There is no doubt that A. ceylanicum from dogs and cats can be transmitted to, and develop into adults in, man. Although a high prevalence of hookworm infection has been recorded in the south of Thailand for several decades, no study of the hookworm species from humans in the south of Thailand has yet been conducted. This study aimed to determine the species of hookworm among schoolchildren in an endemic area in Thailand; furthermore, the study examined the relationship between the estimated worm burden calculated from egg counts and the number of worms recovered in each class of intensity of infection. MATERIALS AND METHODS The study subjects were schoolchildren from primary schools in districts of Nakhon Si Thammarat Province: Paisarn Sathit (Muang district); Sa Bua (Tha Sala district); Put Hong, Thara Wong (Ron Phibun district); and Sa Krai and Don Thore (Chalerm Prakiat district). The feces of these schoolchildren were collected and examined for hookworm eggs by the KatoKatz s method (Katz et al, ). The intensities of hookworm infection were classified according to the number of eggs counted in the entire fecal smear and the calculation of the number of eggs per gram of feces. The worm burden in each child was estimated from the number of eggs per gram. All those infected with soiltransmitted helminths were given mebendazole mg twice daily for days. After medication for hours, all of the feces passed by the hookworminfected children was collected for seven consecutive days. Each daily sample was washed with tap water by simple sedimentation until a clear supernatant was left. The worms were collected and fixed in % glycerine in % alcohol. Only hookworms were separated for study. Daily fixed worms from each individual child were sexed, counted and identified by species using a compound microscope. The total number of worms expelled from each child was compared with the estimated worm burden calculated from the number of eggs per gram by KatoKatz s method. Only complete day fecal samples were used for the analysis of worm burden. All the hookworms obtained from these children were included in the study. Three weeks after medication, all treated children were asked to provide fecal samples for the detection of any uncured cases using the method mentioned above. RESULTS The prevalence of hookworm infection in schoolchildren from the six primary schools is shown in Table. The intensity of hookworm infection was classified as light, moderate, or heavy. Based on a WHO Technical Report (8), these intensities are determined according to the number of eggs counted per gram of feces (NEPG). The worm burdens in each intensity class are then estimated as shown in Table. Thirtyeight subjects delivered complete day stools. Stool samples of light intensity hookworm cases were collected for complete days. The total number of hookworms recovered ranged from to, with the number of males ranging from to and females from to (Table ). Fifteen cases (88.%) expelled a number of worms that corresponded to light Vol No. September

3 SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH Table Prevalence of hookworm infection in six primary schools in Nakhon Si Thammarat Province. Schools No. examined No. positive with hookworm (%) Paisarn Sathit 8 (.) Sa Bua (.) Put Hong (8.) Thara Wong (8.) Sa Krai 8 (.8) Don Thore 8 (.) Total, 8 (.) Table Hookworm burden estimated from the number of eggs per gram (NEPG) of feces in each intensity class. Intensity NEPG Hookworm burden Light infection <, Moderate infection,, Heavy infection >, > intensity infection, ie from to (Table ). The worm count exceeded this intensity interval () in cases (.8%). For the moderate intensity infections, samples of day stool were collected. The number of worms recovered ranged from to 8, with males and females ranging in number from to 8 and to respectively. There were five cases (.%) in which between worms were recovered: moderate intensity. However, cases (8.%) expelled worms below the level of moderate intensity infection () (Table ). For the heavy intensity group, five samples of day stools were collected. The number of worms recovered ranged from to, with males and females ranging in number from to and to. There were no cases of worms expelled at a rate consistent with heavy intensity infection (over ) (Table ). Table Number of hookworms recovered from the day bowel movements of each schoolchildren with light, moderate and heavy intensity infection; after treatment with mebendazole mg twice daily for days. Case No. Light intensity 8 NEPG,,8,,,8,,,8,,8,,,, Moderate intensity 8,,8,8,8,,,8,8,,,,,,,, Heavy intensity,,8,,8,8 Number of worms recovered Male Female Total a a b b b b b b b b b b b 8 8 NEPG = Number of eggs per gram of feces. a Worms recovered above the light intensity interval (). b Worms recovered below the moderate intensity interval (). Vol No. September

4 HOOKWORM INFECTIONS IN SOUTHERN THAILAND Table Relationship between worm expulsion and worm burden calculated from the number of eggs per gram of feces for each intensity of hookworm infection. Intensity Number of cases Number Number not Calculated Worm expulsion corresponding corresponding intensity intensity (%) (%) Light Moderate Heavy Total 8 (88.) (.) (.8) (8.) () 8 Table Hookworm cure rates: days after treatment with mebendazole mg daily for days. Intensity of Number Number infection treated cured (%) Light 8 (8.) Moderate 8 (.) Heavy (.) Total (.) Stool samples of hookworm cases from these six schools were examined days after treatment: the overall cure rate was. % (Table ). The total number of hookworms recovered from schoolchildren from these primary schools was,; there were, male and,8 female worms. All male hookworms were identified as Necator americanus. Of the female hookworms,.8% were N. americanus and only.% ( worms) were A. duodenale. Of the, hookworms,.% were N. americanus and.% were A. duodenale. In total,, male and,8 female N. americanus were recovered, and the M : F sex ratio was :.. All the A. duodenale were recovered from schoolchildren from the Don Thore Primary School. The prevalence of A. duodenale infection in this study was.% ( of 8 cases). However all of these featured coinfection with N. americanus. No A. ceylanicum infection was detected in this study. DISCUSSION This study has shown that Necator americanus is the predominant hookworm in Nakhon Si Thammarat Province, southern Thailand; Ancylostoma sp is a far less significant cause of infection. The result is consistent with those of previous studies (Radomyos and Saovakontha, 8; Areekul et al, b; Harinasuta and Areekul, 8). In the study of hookwormrelated anemia by Areekul et al (b), of the cases were caused by A. ceylanicum. On the other hand, the prevalence of A. ceylanicum in this study was %. One case was of single infection: the patient was a yearold boy who expelled ( male and female) A. ceylanicum; the other cases featured coinfection with N. americanus; there was one case of triple infection (N. americanus, A. duodenale, and A. ceylanicum). Of 8, hookworms examined,.8% were N. americanus,.% A. duodenale and.% A. ceylanicum. Almost all of the cases reported were mixed infections: the predominant species was N. americanus and the associated minor species were A. duodenale, and A. ceylanicum. Ancylostoma species was recovered from patients from the central, eastern and northeastern provinces; patients from the southern province expelled only N. americanus (Radomyos and Saovakontha, 8; Harinasuta and Areekul, 8). Neither A. duodenale nor A. ceylanicum has been reported from the southern provinces by previous researchers (Table ). Vol No. September

5 SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH Table Previous reports on hookworm species in human infection in Thailand. Authors Number of Prevalence (%) Species recovered (%) Cases Hookworms A.d. A.c. N.a. A.d. A.c. Radomyos and Saovakontha8 a Areekul et al,b a Harinasuta and Areekul, 8 a Harinasuta and Areekul, 8 b Anantaphruti et al, c 8 8 8,8 8,,,, a In Hospital for Tropical Diseases; b In Nakhon Ratchasima Province; c In Nakhon Si Thammarat Province; N.a. = Necator americanus; A.d. = Ancylostoma duodenale; A.c. = Ancylostoma ceylanicum. In our study, we found cases infected with A. duodenale, only one worm in each case. No A. ceylanicum was found in the present study. This may be due to the comparatively small sample size in this study; the absence of A. ceylanicum might be explained by the fact that half of the schoolchildren examined were from ThaiMuslim families, which seldom keep domestic pets. The route of transmission of Ancylostoma sp to their normal hosts is mainly oral; infection via the percutaneous route is far less common. A. ceylanicum is also transmitted by the oral route (Yoshida, 8; Yoshida et al, 8) and by the cutaneous route (Areekul et al, a). In areas where dogs and cats are usually kept as pets or where many stray animals are present, there is a high risk of human infection due to the likelihood of contact with pets, their feces, or soil or sand contaminated with infective larvae. Worm expulsion from the schoolchildren did not entirely correlate with the worm burden estimated from the number of eggs per gram of feces. In many moderate, and all heavy intensity groups, actual numbers were lower than those that had been estimated. Many factors may have been involved, such as the lower cure rates of chemotherapy in moderate and heavy infections and the consequently incomplete worm expulsion. In our study, the cure rate of light intensity of infection was higher than those of moderate and heavy infections. Many factors are related to the variability in the number of eggs found in the feces, which influenced the egg count. These factors include fluctuations in the egg output of female worms (Anderson and Schad, 8), the fecundity of worms in the gut (Hill, ), and the uneven distribution of eggs in the stool. In patients with diarrhea, the consistency of the stool sample influences the amount and weight of feces that is examined, leading to errors in the calculation of the number of eggs per gram and in the estimation of the worm burden. ACKNOWLEDGEMENTS The authors wish to thank the Japan Association for Parasite Control (JAPC) and Asian Parasite Control Organization (APCO) for their financial support of this study. REFERENCES Anantaphruti MT, Nuamtanong S, Pubampen S, Rojekittikhun W, Visiadsuk K. Zoonotic potential of dogs intestinal helminths transmitted to man. In: Chen ER, Yamaguchi T, Chung WC, eds. Proceedings of the Sixth AsianPacific Congress for Parasitic Zoonosis. Taipei, :. Vol No. September

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